A major question in neuroscience is how animals translate sensory input into motor output. A particularly good system to address this question is the Drosophila gustatory (taste) system, since both the primary sugar-sensing neurons as well as the motor neurons that elicit feeding are well characterized. When a hungry fly encounters appetizing food, it extends its proboscis and begins feeding. As both the primary sensory inputs and motor outputs are located in close proximity to each other in the subesophageal zone (SEZ) of the Drosophila brain, local circuits in the SEZ likely govern feeding decisions. This proposal intends to identify second-order taste neurons that may bridge sensory inputs and motor outputs. Activation of 7 different candidate second-order taste neurons, similar to activation of the primary sugar sensing neurons, is sufficient to generate feeding behavior. Thus, candidate neurons identified thus far may be involved in the pathway from sensory input to motor output. To analyze the role that second- order taste neurons play in feeding, Aim 1 will determine the anatomical connectivity between first-order taste neurons and candidate second-order neurons, Aim 2 will determine the stimuli that second-order neurons respond to, and Aim 3 will determine the behaviors that second- order neurons mediate. By identifying and characterizing second-order taste neurons, this proposal will build the foundation for understanding how basic sensory information is integrated with internal cues, such as hunger, into behaviors like feeding. An understanding of feeding decisions in insects may provide insights into how to prevent the spread of diseases such as malaria that depend on an insect vector. Furthermore, because flies respond to similar cues as mammals, such as appetizing sugar substances and bitter toxins, understanding the circuits that underlie feeding may shed light into human feeding related disorders such as obesity and diabetes.